The present invention generally relates to apparatus for completing downhole wells, and more particularly relates to sand screen apparatus for filtering particulate matter out of formation fluid entering the well bore to be flowed upwardly through the well flow conductor.
In the course of completing an oil and/or gas well, it is common practice to run a string of protective casing into the well bore and then to run the production tubing inside the casing. At the well site, the casing is perforated across one or more production zones to allow production fluids to enter the casing bore. During production of the formation fluid, formation sand is also swept into the flow path. The formation sand is relatively fine sand that tends to erode production components in the flow path.
In some completions, the well bore is uncased, and an open face is established across the oil or gas bearing zone. Such open bore hole (uncased) arrangements are utilized, for example, in water wells, test wells and horizontal well completions.
One or more sand screens are typically installed in the flow path between the production tubing and the perforated casing (cased) or the open well bore face (uncased). A packer is customarily set above the sand screen to seal off the annulus in the zone where production fluids flow into the production tubing. The annulus around the screen is packed with a relatively coarse sand (or gravel) which acts as a filter to reduce the amount of fine formation sand reaching the screen. A work string and service seal unit (SSU) is used to spot the packing sand around the screen.
During well completion, packing sand or gravel is also pumped and squeezed into the producing formation around the screen for filtering unconsolidated material out of the inflowing well fluid. The packing sand is pumped down the work string in a slurry of water or gel and is spotted directly under the packer or above the sand screen. The packing sand also fills the annulus between the sand screen and the well casing. In well installations in which the screen is suspended in an uncased open bore, the sand or gravel pack supports the surrounding unconsolidated formation.
Sand screen structures are typically constructed, prior to their operative placement in a well bore, from a plurality of generally tubular axial filter sections disposed in an end-to-end orientation in which facing end portions of each axially adjacent filter section pair are threadingly secured to a connection collar member interposed between the two filter sections. After the assembled multi-section sand screen structure is coaxially placed in the well bore, the packing sand/gel slurry is forced down the well bore/sand screen annulus to form, in effect, a prefiltering barrier around the sand screen to inhibit the entry thereinto of fine formation sand.
A problem potentially encountered in this sand packing process is the formation around the sand screen of annular sand "bridges" that may prevent the complete circumscribing of the screen structure with packing sand in the completed well. This incomplete screen structure coverage by the packing sand, of course, leaves an axial portion of the sand screen exposed to the fine formation sand, thereby undesirably lowering the overall filtering efficiency of the overall sand screen structure.
One conventional approach to overcoming this packing sand bridging problem has been to provide each generally tubular filter section with a circumferentially spaced series of open-ended shunt tubes that longitudinally extend axially through the interior of the filter section, with opposite ends of each shunt tube projecting outwardly beyond the active filter portion of the filter section. In the assembled sand screen structure the shunt tube series are axially joined to one another and form a shunt path extending along the entire length of the sand screen structure and operative to permit the inflowing packing sand/gel slurry to bypass any sand bridges that may be formed and permit the slurry to enter the screen/casing annulus beneath a sand bridge and form the desired sand pack beneath it.
This conventional solution to sand bridging, however, carries with it several well known problems, limitations and disadvantages. For example, the use of thread joints to interconnect each axially adjacent pair of filter sections often makes it difficult to circumferentially align each pair-of shunt tube series that must be interconnected to maintain axial continuity in the overall shunt flow path. Additionally, a supplemental connection fitting, interposed between the facing ends of each axially adjacent pair of shunt tube series, must be used to interconnect and operatively communicate the interiors of the shunt tube series.
This conventional necessity, coupled with the requirement of using a connection collar to couple the bodies of each adjacent pair of filter sections, tends to make the assembly of the overall sand structure relatively difficult and time consuming. Moreover, the necessity of using these two connection fittings between each axially adjacent pair of filter sections increases the "blank" spaces between the active filter portions of the filter sections. This, in turn, undesirably reduces the filtration capacity per length of the assembled sand screen structure.
It can readily be seen from the foregoing that a need exists for a multi-section sand screen structure that eliminates or at least substantially reduces the above-mentioned problems, limitations and disadvantages commonly associated with conventional sand screen structures of the general type described. It is accordingly an object of the present invention to provide such a sand screen structure and associated assembly methods therefor.